Vulnerability of the savannahs of central Africa facing the last millennium climate: Insight from Lake Petpenoun (Cameroon) pollen, charcoal and carbon isotope record

Abstract

A study of the pollen content and organic matter of a 6 m long core recovered from the gallery forest alongside the tributary of Lake Petpenoun, not far from its mouth (NW Cameroon, 5°38′29.3 N, 10°38′43.1E, 1120 m asl) documents the evolution of the « Grassfields region » over the last millennium. The exceptional rate of accumulation of the sedimentary series, where the last millennium is 5 m thick, allows to differentiate two distinct periods. Between 900 and 1420 CE, the coring site was located under lake water, reflecting the expansion of the lake under humid environmental conditions during the Medieval Climate Anomaly (MCA). The coring site then gradually dried up from 1420 CE onward, during the Little Ice Age (LIA). Then, in 1850 CE, modern conditions were established. During the LIA, the lake edge moved about 140 m downstream of the coring site due to drying conditions. The date of 1420 CE corresponds to a major event that affected not only local hydrological conditions but also regional vegetation. The collapse of pollen production shows the general degradation of the landscape due to increased drought conditions.